1. Field of the Invention
The present invention relates to an apparatus for generating an optical fiber laser capable of tuning a wavelength thereof, and more particularly to an apparatus for generating an optical fiber laser of which the wavelength can be tuned by a cholesteric liquid crystal cell inserted into a ring type laser resonator.
2. Description of the Prior Art
In the optical communication, to transmit a mass-information with maximum utilization efficiency of the established optical lines, an optical transmission method that transmits an optical signal with varied wavelength is being used. This is called a wavelength division multiplexing (WDM) optical transmission technique.
For this transmission method, various types of light sources such as a semiconductor diode, an optical fiber laser, or a solid laser have been studied and developed worldwide, however, these sources have limited wavelength varying range and their production processes are difficult, thereby they have limited applicability.
A typical ring type laser comprises a 20 m light amplify fiber (LAF), a 60 m dispersion shift fiber (DSF) for non-linear polarization effect, a light direction controller, an optical fiber coupler for input light, a linear polarizer for wavelength tuning, and a polarization controller composed of two birefringence controllers. A 980 nm-wavelength laser diode is used for pumping, and a wavelength division optical fiber coupler is installed at an end of a light amplify fiber.
A light with a wide distribution range, produced by pumping at the light amplify fiber, is converted to a light with a resonance-capable polarization state by the linear polarizer and the birefringence occurring at the dispersion shift fiber. Thereafter, the wavelength of said oscillated light, with a resonance-capable polarization state, is changed by a birefringence controller. However, a prior ring-type laser resonator has a problem that the applicable wavelength range of the light for the birefringence controller is limited. (C in FIG. 3)
Therefore, it is difficult to transmit mass information through a limited optical line and costly to transmit information.
To solve the problems that the wavelength tunable range of the prior art is narrow and the production procedure is difficult, it is therefore the object of the present invention to provide a wavelength tunable optical fiber laser, which is able to enlarge the wavelength tunable range of an oscillated laser by increasing the gain variance in a resonator by inserting a cholesteric liquid crystal converging element into a ring type laser resonator.
To achieve the object, an apparatus for generating an optical fiber laser capable of tuning a wavelength thereof in accordance with the present invention comprises a pump laser to pump the light with changed polarization state, a light amplify fiber to produce a seed light using the pumped light from the pump laser at a certain operation wavelength and thereafter, when the seed light has stable frequency, to put out the light in that wavelength, a dispersion shift fiber to give a non-linear polarization effect to the output light from the light amplify fiber, a linear polarizer to tune the wavelength of the light from the dispersion shift fiber within a wavelength varying range, a light direction controller to give a certain oscillation direction to the tuned light, a optical element converging a light beam, with a cholesteric liquid crystal cell inserted, which transmits only a circularly polarized light having a consistent rotation period with the rotational direction of the liquid crystal surface and reflects all the rest of the light, and an output port to confirm a laser output light beam by putting out a certain portion of the light from the light converging element.